1. Field of the Invention
The present invention relates to mobile communication and, particularly, to a mobile communication system involving a mobile base station that is installed in, for example, a train to provide value-added services to mobile units such as cellular phones and pagers that are present in a mobile space formed in the train. The present invention also relates to a method of controlling such a system and such a mobile base station.
The present invention allocates a mobile radio zone to a mobile space defined in, for example, a public transport unit such as a train or a bus, and provides specific services only to mobile units that are present in the mobile radio zone.
2. Description of the Related Art
There are no prior arts that employ the concept of assigning a mobile radio zone to a mobile space so that the mobile radio zone may travel together with the mobile space. This concept is advantageous in clearly separating the inside of the mobile space from the outside thereof.
The prior arts employ fixed radio zones, which are unable to separate subscriber terminals that are present in the mobile space from those that are present outside the mobile space. The prior arts, therefore, are unable to provide exclusive services only to subscriber terminals that are present in the mobile space.
FIG. 1 shows a mobile communication system according to a prior art.
An existing base station 10 (A) has a fixed radio zone 20 (CzA) in which a mobile space 30 (B) travels. The mobile space 30 accommodates mobile subscriber terminals 40 and 41 (a, b). A mobile subscriber terminal 42 (c) is inside the zone 20 but outside the mobile space 30. The existing base station 10 provides communication services to the subscriber terminals 40 to 42.
The existing base station 10 directly controls the subscriber terminals 40 to 42 with regard to their call and speech signals and, therefore, cannot know whether the subscriber terminal 40 is inside or outside the mobile space 30. The existing base station 10 simply provides the same services to all of the subscriber terminals 40 to 42 without discriminating the subscriber terminals 40 and 41 that are inside the mobile space 30 from the subscriber terminal 42 that is outside the same.
If the mobile space 30 wants to provide the inside thereof with specific services such as arrival time notification, the mobile space 30 must have devices to display the information, or passengers in the mobile space 30 must have special receivers to receive the information. Such display devices involve costs, which may be absorbed by displaying corporate advertisements thereon. The costs of such special receivers, however, must impose a burden on passengers.
Instead of the special receivers, the existing base station 10 may employ standard subscriber terminals to use special dial services. The mobile space 30, however, travels along a route where there are radio blocking objects such as high buildings and tunnels. It is impossible for the existing base station 10 to secure stable communication for the subscriber terminals in the mobile space 30 that travels along such a radio blocking route.
When the mobile space 30 moves from the zone 20 to the next zone 21 at a high speed, channel switching and position registering processes simultaneously occur between the existing base stations and the subscriber terminals in the mobile space 30, to maintain communication between them. This may temporarily congest a network that connects the existing base stations to one another. At the same time, each subscriber terminal must scan perch channels to exhaust the battery thereof.